Adv 2.0 L5a: skills migration off AdvCharacter to player_meta

Eight player_meta columns (combat_level, combat_xp, mining_skill,
mining_xp, foraging_skill, foraging_xp, fishing_skill, fishing_xp).
SkillState struct with HasSkills() marker mirrors PetState/HouseState
shape. loadSkillState / upsertPlayerMetaSkillState /
backfillPlayerMetaSkillState / skillStateFromAdvChar helpers.

Dual-writes wired at every mutation site: consumables craft XP (both
success and failure branches), events.go XP grant across all skills,
arena death + session-complete combat XP. Backfill is idempotent (only
fills rows where every skill column is still zero AND the legacy row
has any non-zero value).

CombatLevel/CombatXP are transitional — dropped at L5g after the DnD
mass-backfill retires the legacy CombatLevel-derived fallback.

Tests: TestPlayerMetaSkillStateBackfill_Idempotent,
TestLoadSkillState_FallsBackToAdvCharacter,
TestUpsertPlayerMetaSkillState_RoundTrip.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/plugin/adventure_events.go

@@ -215,6 +215,7 @@ func (p *AdventurePlugin) handleEventRespond(ctx MessageContext) error {
 			}
 			checkAdvLevelUp(char, xpSkill)
 			_ = saveAdvCharacter(char)
+			_ = upsertPlayerMetaSkillState(ctx.Sender, skillStateFromAdvChar(char))
 		}
 	}